1. Field of Invention
The present invention relates generally to railroad crossings having precast concrete panels and methods for making such crossings and, more particularly, to such crossings which are curved and include a restraining rail cast into place to restrict the lateral movement of train or railcar wheels as the train travels through the crossing.
2. Brief Description of the Prior Art
When a roadway crosses railroad tracks, a crossing must be constructed to permit traffic to pass over the tracks as smoothly as possible. Typically, the top surfaces of each of the tracks are in substantially the same plane as the roadway on either side of the tracks. A recessed area between the tracks and to either side thereof are built up to street level with the exception that recesses must be provided adjacent the upper portion of each track to accommodate the flanges on railcar wheels.
Timber, asphalt, and poured concrete are examples of prior art materials which have been used to construct railroad crossings. Frequently, maintenance must be performed on these railroad crossings. This may be occasioned by the resurfacing of the street, the need to remove or replace the rails, or the settling of the rail bed. With these types of railroad crossings such maintenance can be extremely expensive and labor intensive.
Precast concrete crossings avoid some of these difficulties by using a plurality of modular concrete sections to form the railroad crossing. One type of prior art precast concrete crossing includes precast structures which are received under the railroad track in the crossing and which substitute for the railroad ties that support the track on either side of the crossing. Another type of precast concrete crossing includes precast structures which are supported on ties in the crossing adjacent railroad track which is also supported on the ties.
One example of the latter type of precast concrete crossing is disclosed in U.S. Pat. No. 5,191,657 to Davis for a composite rubber/concrete railroad grade crossing system. In Davis, substantially rectangular precast panels have a metal corner portion made of angle iron, cast into the panel around the upper perimeter thereof. Elastomeric pad units abut either side of each rail with a plurality of central precast concrete panels laid end to end in the center and narrower precast concrete panels laid end to end on the outer sides of each track. The panels thus hold the elastomeric portion in place and are, in turn, restrained from longitudinal movement along the tracks by brackets which are bolted to the ties and which abut the panels at each end of the crossing.
The metal corner portions are provided to prevent the concrete corners from crumbling as a result of traffic passing thereover. In some prior art installations using similar panels, the metal corner portions on adjacent panels are welded together to prevent independent movement of separate panels.
Precast panels for use in grade crossings such as those shown in the Davis patent are created using a rectangular mold. A rectangular angle iron frame is placed on an upper portion of the mold. Thereafter concrete is placed in the mold to the level of the top surface of the frame thereby casting the metal frame into the upper surface of the panel.
Another example of a precast concrete crossing is disclosed in U.S. Pat. No. 4,641,779 to O'Brien et al., for a concrete grade crossing system. In O'Brien, a modular railway crossing structure supports a pair of rails. The rail bed unit in O'Brien comprises a bed member which is wider than the track, and two opposed center panels which are mirror images of one another. The base member has a central recess which is approximately as deep as standard rail and the walls of the recess are shaped to conform generally to the rail. The width of the central recess corresponds to the desired gauge of the railway. The two center panels are designed to fill the remainder of the central recess in the base member and are placed in abutting relation in the recess. The outer edge of each member conforms to the profile of the rail in like manner to the walls of the recess in the base member. These central units are bolted in place to the base member to form a railroad crossing bed unit. A complete railway crossing is constructed by placing a plurality of such units in abutting end-to-end relation. The base member and center panels are manufactured using two rectangular forms. Concrete is poured into these rectangular forms to mold the bed unit and the center panels.
Problems exist with both types of precast concrete crossings. The metal corner portions disclosed in the Davis patent creates a conductor capable of shunting currents between the rails which can create signalization malfunctions. Such prior art panels include opposing metal corner portions which are each within a few inches of an adjacent rail. In the presence of salt and water, specially in freezing temperatures, a conductive path between the rails is easily set up whether or not the corner portions are welded to one another.
The welds in the Davis patent are also problematic when maintenance is required on the railroad bed in the crossing. This requires that the panels be removed, which in turn, requires breaking the welds on any of the panels that are welded together. After maintenance of the bed, the panels are returned to the crossing re-welded.
Additionally problems arise when the crossing is curved. Both Davis and O'Brien provide for rectangular precast concrete panels, each piece molded to have identical dimensions. Rectangular shaped panels are not appropriate for use in curved crossings because they do not fit tightly together when laid end-to-end on a curve leaving wide gaps between panels. An improvement has been to use wedge-shaped panels having identical dimensions instead of rectangular panels to form curved crossings. When wedge-shaped panels are laid end-to-end to form curved crossings, facing in between adjacent panels results because the dimensions of the panels are not varied in proportion to the radius of curvature of the crossing curve. Facing between adjacent wedge-shaped panels reduces the durability of the crossing.
Curved crossings present yet another problem. When a railroad car moves across a curved area, the train or railcar wheels which travel on the inside curve rail is pulled towards the outside of the curve due to the centrifugal forces acting on the train or railcar. These forces cause the train or railcar wheels traveling on the inside curve rail to exert additional forces on the center panels which limit the life of the crossing.
Even further problems arise when curved crossings are poured in place. For example, the roadway is out of service longer than if precast panels are used because of the time required to dry the concrete crossing. The quality of crossings poured in place is more difficult to control than that of panels precast in a controlled environment. Thus, curved crossings that are poured have reduced durability and exhibit higher wear. Installation of such crossings creates serious traffic disruptions. Also, quality for poured crossings varies.
Also discussed in the O'Brien patent is the use of an elastomeric boot in connection with a precast concrete crossing. In the O'Brien system, the boot entirely encases the flange or lower portion of each rail. The boot extends from the flange along each side of the rail and terminates on both sides of the rail, at a point just beneath the head or upper portion of the rail upon which a train wheel is supported. While the boot disclosed in the O'Brien patent works well to cushion the rail against abrasion and vibration, because the entire head of the rail is exposed, there may be electrical conductivity between the rail and the precast concrete in which it is secured. This condition is aggravated in regions where salt is applied to roads in snowy and icy weather by increasing the conductivity of water accumulating on the crossing. When the rail is not electrically isolated, it cannot be effectively used as a signal conductor. In addition, current flowing between the rail and the concrete accelerates corrosion. When the O'Brien system is used, access to the rails can be had by removing the central panels. This permits repair and replacement of the boot. It would be desirable to provide such access on a curved crossing.
It would also be desirable to provide a precast concrete panel for use in grade crossing on a roadway which overcomes problems associated with prior art crossings.
It would also be desirable to provide such a crossing which can be easily removed and replaced for maintenance to the rail bed beneath the crossing.
It would also be desirable to provide such a crossing which reduces signalization problems.
It would also be desirable to provide such panels for use in curved crossings which eliminates facing between adjacent panels.
It would also be desirable to provide such panels with increased durability.
It would also be desirable to provide such panels with a restraining rail coupled to the standard rail to provide increased rigidity.
It would also be desirable to provide such panels with a restraining rail coupled to the standard rail to restrict the movement of train or railcar wheels as they travel through the crossing.
It would also be desirable to provide such a crossing in which an elastomeric boot is used to provide electrical isolation.
It would also be desirable to provide such a crossing in which the boot is easily maintained and replaced.
It would also be desirable to provide such a crossing which minimizes road disruption.
It would also be desirable to provide a method for making such a panel.
It would also be desirable to provide a method for making a curved crossing with a high degree of quality control.
It would also be desirable to provide a method for making such panels that would minimize process variations from panel to panel.